A device as indicated in the opening paragraph is described in the non-published patent publication EP 10166885.3 filed in the name of Applicant. The herein described OLED has a substrate of glass, on which respectively a first electrode layer of ITO, a package of layers comprising electroluminescence material (ELP) and a second electrode layer of Al are deposited. Said ELP is composed of a number of different sublayers, including at least an emission layer and a conductive layer. Upon applying an appropriate voltage between both electrode layers, the ELP emits light. Depending on the type of the electroluminescence materials used in the ELP, different light spectrums (colors') can be generated. The described layer package is contained in a cavity formed by a bowl-like cover. This cover is secured at its rim to the glass substrate by means of a sealing material.
The described OLED further contains a spacer layer (referred to in the previous application as ‘separating foil’), which lies loose between the cover and the second electrode layer. Said spacer layer can act as a compliant protection layer which should prevent direct contact between the cover and the ELP. Such contact can cause mechanical damage to one of the electrodes or shorting. This holds especially when moisture-absorption means are provided on the inside surface of the cover. The spacer layer is made of a resilient material (such as polyethylene or Si-containing polymer).
The here-described OLED is of the so-called ‘cavity-lid’ type, in which the ELP is contained in a bowl-like cover. Another type of OLEDs is commonly referred to as the ‘flat-lid’ type. In this type, one of the substrates is usually glass or plastic whereas the other substrate (still often referred to as the ‘cover’) can be made by a relatively thin layer of glass material or of metal.
Although the described OLED in general shows good properties, there still exists a need for further improvements. This holds especially the sealing between the cover and the substrate. Good sealings are essential for a long functional life-span of the OLEDs. Such sealings should especially prevent the penetration of moisture into the OLED cells, as the OLED material is readily degraded by moisture. The general desire to manufacture larger OLED cells requires new approaches in the sealing of the cover to the substrate.